Although electromechanical switching devices, commonly referred to as relays, have been used for many years, there is a continuing need for such a device which is small in size, yet capable of reliably handling relatively high current switching jobs. This requirement for miniaturization together with reliability has become particularly important in recent years because of the increasingly common practice of mounting relays on printed circuit boards.
In the design of an electrical relay, and other such electromechanical devices, a most important consideration is the design of the "magnetic circuit." The design of an effective magnetic circuit determines to a great extent the current switching capability of the relay and the power needed to operate it. The magnetic circuit of a relay generally includes the core of the relay coil, the relay frame, the armature that moves the relay contacts, and the air gaps that exist where the core of the relay coil and the armature interface with the relay frame and most importantly between the armature and the core of the coil.
In relay operation, an electrical current through the relay coil sets up a magnetic field in this magnetic circuit; and it is the strength of the magnetic field in the air gap between the armature and the core of the relay coil that moves the armature into contact with the core of the relay coil, thus providing the motion to operate the switching contacts of the relay. In the relay, the core of the relay coil, the frame, and armature are all materials easily magnetized, such as steel. The air gaps, however, present a high reluctance, i.e., impedance to the establishment of the magnetic field; and the air gap between the armature and the core of the coil has by far the most significant reluctance in the magnetic circuit. In obtaining switching capability for the relay, it is desirable to design for effective contact travel distances and rapid movement of the contacts by the armature. It is also desirable to provide the strongest possible magnetic field at this armature gap for the available relay current to provide for positive and rapid contact movement and to permit the use of a strong spring for return movement of the armature when the relay current is stopped, also for positive and rapid contact movement.
Thus, the mechanical arrangement of the magnetic coil core and relay armature and resulting air gap and the design of their interfaces significantly affect the ability of the relay to perform its function as an electrical switching device. It is desirable to reduce any air gap between the core of the relay coil and the relay frame to a minimum, provided, of course, that the relay can be manufactured at a cost consistent with its intended application and market. At the closable air gap between the movable armature and the core of the coil, however, there is the problem of providing an air gap of sufficient length to provide an effective switching and circuit breaking capability for the relay contacts and of providing an air gap short enough for low magnetic reluctance and a strong magnetic field for operating effectively, in conjunction with the relay spring, the switching function of the relay.
As in other fields, there is also a continuing effort to find ways to reduce the cost of manufacturing relays. In the prior art, this has been difficult to achieve to any meaningful extent because most existing manufacturing procedures require a significant amount of human participation, especially in connection with the usually necessary step of finally adjusting the positions of the various relay components with respect to one another after the relay has been assembled to ensure effective switching and efficient operation of the relay.
Specifically, in the prior art, the core of the relay is usually fastened to the relay base or frame by staking or some similar procedure in which the position of the core relative to the frame is essentially preset by the nature of the fastening operation and is incapable of being adjusted either during or after the fastening procedure. Accordingly, in order to correct for overshoot of the movable contact arm and, in particular, to assure correct positioning of the armature relative to the core and of the movable contact button relative to the stationary contact members, it is usually necessary to manually bend or twist the spring that supports the armature and the movable contact button to some extent after the relay has been assembled.
A relay design and manufacturing process that achieves correct positioning of the various relay components with respect to one another substantially automatically with minimal operator participation would provide a meaningful reduction in manufacturing costs, and be of significant value.